At pH values above 7.5, the disinfectant capability of chlorine is
greatly reduced
Chlorine's disinfecting power in water depends on the relative proportion of two chemical species formed when chlorine dissolves in water: hypochlorous acid (HOCl) and the hypochlorite ion (OCl-).
HOCl is an uncharged, small molecule that can penetrate microbial cell walls efficiently, making it a far more powerful disinfectant, whereas the negatively charged OCl- ion is repelled by the negatively charged surface of bacterial cells and is therefore a much weaker germicide, often cited as 60-80 times less effective than HOCl.
The equilibrium between HOCl and OCl- is strongly pH-dependent: at lower pH (below about 6.5-7), HOCl dominates, while as pH rises, the equilibrium shifts progressively toward OCl-.
At pH values above 7.5, the dissociation strongly favours OCl-, so the proportion of the more effective HOCl drops sharply.
Consequently, the disinfectant capability of chlorine is greatly reduced at pH above 7.5, which is why water and wastewater treatment plants generally try to maintain slightly acidic to near-neutral pH for effective chlorination.
Similar Questions
Give below are two statements:
Statement I : Thermal pollution, usually effluent from cooling systems of power plants or other industries, alters water temperature in a lake or stream.
Statement II : Humans also cause thermal pollution by altering vegetation cover and run-off patterns.
In the light of the above statements, choose the correct answer from the options given below:
Major contributor to carbon monoxide emissions in metropolitan areas of India is/are:
The most important pollutants that cause degradation of water quality in rivers and streams are
(a) Bacteria
(b) Nutrients
(c) Metals
(d) Total dissolved solids
(e) Algae
Choose the most appropriate answer from the options given below:The most dominant source of Benzene emissions in ambient air is
Major sources of oxygen demanding waste in fresh water systems are
(a) Agricultural run-off
(b) Food processing
(c) Ore mining
(d) Sewage effluent
(e) Landfill sites
Choose the correct option from those given below: -
Which of the following pollutant gases is not produced both naturally and as a result of industrial activity?
Which of the following pollutants is the major cause of respiratory diseases?
Assertion (A): In urban areas, smog episodes occur frequently in winters.
Reason (R): In winters, a lot of biomass is burnt by people for heating purposes or to keep themselves warm.
Choose the correct answer from the code given below:
With increase in temperature, the dissolved oxygen content in a water body will:
In the formation of Surface Ozone, which of the following do play an important role?
(a) Oxides of nitrogen
(b) Oxides of sulphur
(c) Sunlight
(d) Carbon monoxide
Choose the correct answer from the code given below:
Important Questions from Pollution
Which of the following isnota common component of photo-chemical smog?
Which of the following is NOT the main objective of Ganga action plan?
Which of the following pollutants causes water pollution ?
Presence of which pathogenic microbe in water is indication of contamination?
Which of the following isnota vehicular pollutant?
